Readers' Answers (1)

Eventually, almost everything spoils/rots, but catnip is dried and should last longer than many other products. However, once the bag is open, the catnip will lose its potency and thereby lose its attractiveness to cats. Your cats may actually refuse to eat it if you offered it to them because it would not have the fresh catnip smell.

Catnip is inexpensive and your catnip is old (according to you, "a couple years"). Personally, I'd throw it out at this point and buy a new bag. (I honestly don't know if old catnip is truly harmful, but it is better to be safe than sorry.)